AWS KMS is a Key Management Service that lets you create Cryptographic keys that you can use to encrypt and decrypt data and also other keys. You can read more about it here.
Important Points About Keys
Please note that the CMK generated can only be used to encrypt a small amount of data like passwords, RSA keys. You can use AWS KMS customer master keys (CMKs) to generate, encrypt, and decrypt data keys. However, AWS KMS does not store, manage, or track your data keys, or perform cryptographic operations with data keys.